Punishing Chaotic Stupid ?

[Claudius Maximus]

If this guy is just having trouble playing serious or reasonable characters, but you and your other players are open-minded, you could try to make the game more lighthearted and random, to better suit his playstyle. Make sure the other players are amenable to this idea though.

If he's acting like this and ruining a serious campaign, then he's being a jerk. Tell him his actions are having a negative effect on your and the other players' enjoyment of the game, preferably in a calm manner. If he persists in full knowledge of that fact then he's a double jerk, and you might be better off not including him in your game.

In game punishments, in the form of DM fiat to hurt his character as punitive action for the way the player is conducting things, is a bad idea. A slightly better alternative is to have the NPCs simply react in a realistic way to his shenanigans. So if he tries to kill the good king on sight for no reason he should be executed, because that's seriously what would most likely happen. You're still not getting at the root problem though, which is an out of game issue.